Your family dynamic sounds a lot like mine although mine was not nearly as severe as yours.
You and your sister were the scapegoats and your other sibling was the golden child that could do no wrong.
My oldest brother and I got the short end of the stick literally and my other brother is the favoured one. The oldest was smart enough to leave the Jws before he was baptized.
Even though I am still in there is no point in talking to my mother. I am a failure in her eyes. Any thing that I accomplish she puts me down. I'm never good enough for her. So I ignore her. It really pisses her off because she can't control my life.